Over a period of several years, the Applicant for this patent has developed numerous inventions for improving the effectiveness of horizontally-installed roadway-marking strips, especially as regards the visibility of the strips under such adverse conditions as darkness and rainy weather.
Among these inventions, there is one covered by Italian Pat. No. 811,581, dated May 2, 1968, and U.S. Pat. No. 3,587,415, plus many Italian patents, applications and several corresponding patents granted in the U.S. All these inventions brought about a gradual improvement in the optics incorporated in the marking strips. The retro-reflecting capability of the optics was improved so that a greater percentage of light was reflected back to the driver from the headlights, the optical service life was extended and, also, the marking strip acquired anti-skid properties. Italian Pat. No. 24096 A/76, filed on June 9, 1976, concerned a further improvement: a retro-reflecting globule (also referred to hereafter as "asymmetrical pearl"). The special, asymmetrical shape of the pearl improved the optical characteristics, which were further enchanced by a layer of microspheres covering the underside of the globule. Other patents corresponding to this Italian patent were also obtained in the U.S., with U.S. Pat. No. 4,072,403, and in several other countries including Great Britain, Sweden and Canada.
More inventions followed, which concerned the method of depositing the optical elements and the relative equipment to do this, and ways of improving the optical efficiency of the elements as, for example, by making them have a double asymmetry.
A special application method and relative applicating device have also been developed, whereby the optical elements can be deposited onto the horizontal roadway-marking strip in a predetermined alignment pattern, thus obtaining maximum efficiency. These inventions are covered by U.S. Pat. Nos. 4,279,534, dated July 21, 1981, 4,322,177, dated Mar. 30, 1982 and 4,369,001, dated Jan. 18, 1983.
A further step ahead was made by reducing the calendered ribbon of retro-reflecting elements to transverse strips, thus producing a product which is particularly suited for marking large surface areas. The transverse strips are primarily supported on rubber sheets, as shown in U.S. Pat. No. 2,013,265, dated Mar. 3, 1982, obtained in Great Britain.